Add documentation for the forceCommit API

[lrao-stripe]

It would be great to add user-facing documentation for:

• ​/tables​/{tableName}​/forceCommit: Would be useful to know how it works and what happens when it fails
• /tables/forceCommitStatus/{jobId}: Would be useful to know how status of the jobs changes/how they're cleaned up

[Jackie-Jiang]

cc @matthewhelmke

[matthewhelmke]

Thank you!